Notice period with the employer

Dear Expert, kindly advise, My son is working in Hyderabad in a leading private banking firm as confirmed employee for last 2yrs, in a junior management position, got another opportunity with a MNC firm. He has submitted resignation a month back and asking his current employer to relieve him on 20th of this month (will complete 35days by that time). His offer with the next employer will expire on 23rd otherwise cannot join afterwards. Next employer will accept relieving letter / resignation acceptance with date of relieving mentioned in it but before joining date. DOJ can not be extended that was clarified before sending offer letter. As per the termination policy "either Bank or Employee will be required to give three months notice in writing or salary in lieu of notice. The decision as to whether or not to accept salary in lieu of notice period will be solely at the discretion of the management " He is requesting management to relieve him considering his leave balance and also willing to pay balance notice period pending if any. But the Management (Managers+next level) is asking him to serve the notice period of 90days with an intention that he will loose the opportunity and continue. But my son is not willing to work even after 90days of notice period and in such case will loose job on both sides. in this case how we can proceed if bank is not ready to relieve on the requested date? what action he can claim in this case when they are not relieving of his choice time and loosing job opportunity? Can any employer make employee to force continue working when he is ready to compensate ? Thanks tvrao161@hotmail.com